Radio volume control



March 26, 1940. J GETAZ 2,194,935

RADIO VOLUME CONTROL Original Filed llay 9 1936 Patented Mar. 26; 1940"UNITED STATES P'AreNfrfor -"icE- ..5itfi2....:..;

Application May 9, 1936, Serial No. 7.8.808

- Renewed August 28,1939

20 Claims. (01. 250-6) This invention relates to the electricaltransmission of intelligence signals, such as sound signals andparticularly to the control of the volume of the sound'received. v

The purposes of this invention are as follows:

1. To control this volume of sound as received so that it will beindependent of the strength of the received signal. i I 2. To controlthis volume of sound as received so that it will be independent ofcontractionsin volume which may be made at the transmitting station bythe transmitting operator.

3. To control the volume of sound as received so that the receiving setwill have small amplification when no signal is being received.

4. 'To automatically maintain the, same volume of sound received inchanging from one transmitting station to another station of differentstrength. I

5. To provide means for controlling the volume of sound at the receivingset so that the volume of sound as received will be proportional to thevolume of sound as originally produced.

In Fig. l is shown diagrammatically the connections to provide for suchcontrol at the broadcasting station.

In Fig. 2 is shown the connections for the re- 1 ceiving set.

The basic principle involved in obtaining such volume control is toutilize an arrow band of frequency, and at the transmitting station togenerate waves within this band so that the frequency of the-waves willvary with the volume of the sound produced. These waves'constitutesignals denoting the volume of the original sound and are used in radiotransmission to modulate the carrier wave, and may be referred to asvolume signals. The carrier is thus modulated in two Ways, it containsthe regular modulation which corresponds in, frequency and amplitudewith the original sound, and in addition it carries another modulationconsisting of these ,volume signals, In the transmitting wave, theamplitude of these volume signals'is not of particular im-' portance,except that they should produce a fair amount of modulation Theirusefulness depends on thevariations of their frequency, and we thus havealong with the usual signals, a special band of signals representingvolume by frequency ratherthan by amplitude.

The principles of this invention may be applied to any means for thetransmission or reproduction of sound in which electrical signals areused to represent the sound waves. These principles may-be used forcontrolling the amplification of electrical signals representing soundwaves which are .reproduced from. phonograph records or motionpictureffilms. a r

To avoid distortion of the regular signals, these volume signals may beconfined to a band below 5 audible frequency,.from a fraction of onecycle per second toabout twenty-five cycles.

In Fig. 1 the microphone! s supplied with current by the battery 2 andisgconnected by the transformer 3 to the amplifying circuit consist- 10ing of the batteryta the tr-iode All and the battery 45, thiscircuitincludes the transformer 38 which connects to" the transmittervmodulator through theline'43.. -u

This transformer 3 lS;8i1S0' COl'1IleCted to the 15 amplifying circuitconsisting. of the battery 4, the battery t, the triode 5, andthetransformer l. The current from the transformer 1 is rectified by thediode I0, thus producing a' direct current envelopewhich correspondswith the variation in '20 volume of the; current generated in themicrophone circuit. In the circuitof this diode l0 isa a: resistance 8shunted by a condenser 9, andthe ends ofthisresistanceare conn'ectedto-the grid I k and fii'amentlorthetriode l2. By varying re- 25'sistance 8 andthe-capacity'ofthe condenser 9 it is possible to. controlthe-frequencywith which .the rectifierwillfollowthe volume change. The

circuitfof this triode; l2 amplifies the voltage variationsinetheenvelope produced byfthe diode 3o llL and thisYcircuit containscthebattery II, the

battery l4, the.zchoke -coil l3, and the saturation triode33 byconnections to the transformer 23..

Another oscillatingcircuit consists of the triode 30, the feed:backpoils 25 and 2B, the condenser 21, the battery 3] and the resistance-29, Which 45 is by-passed. by the condenser'28. The circuit isadjustedt'o produce oscillations of about the same frequency .as thoseproduced by the tube I9 and is connected to the grid of the triode'33 bythe H transformer ,24. circuitmaintains a. con- 50 stant frequency. I .fv

.The' frequency of the beats between these two oscillating circuits'variesas the frequency'of the I oscillations; .producedby tubegla, isvaried bythe I v saturation reactor [5. By proper adjustment of the twooscillating circuits the frequency of these beats may be made to varyinversely with the amplitude of the direct current envelope and they maybe confined to a narrow band below the audible frequency. Theoscillations of these two circuits are rectified by triode 33 in thecircuit consisting of the battery 32, the battery 46 and the condenser34, and the beats are transmitted through the transformer 35 and the lowpass filter 36, which filters out anyharmonics. These low frequencybeats are connected through the transformer 31 to the line 44 leading tothe transmitter modulator. The connection 44 is set on the resistance 42to fix the amplitude of the volume signals, and the line 43 may bevaried in its connection to the resistance 4!, so as to vary themodulation of the main signals. Thisjvariation does not affect themodulation which is made by the volume signals.

In Fig. 2 the signals are received from the antenna 50 through thetransformer 5| and are amplified in two or more circuits consisting ofthe pentode 54, the battery 55, the condenser 52 and the tuningcondenser 53, and transformer 56, also the pentode 59, battery 60,condenser 57, tuning condenser 58, and transformer GI. These signals arerectified by the diode B5, in the circuit containing the tuningcondenser 62, the rcsistance 64, which is by-passed by the condenser 53.The audio frequency is amplified in the circuit containing the triode61, the battery 68, the battery 66, and the transformer 69. From thetransformer 69, the main signals pass through the high pass filter 10which admits all frequencies in the audible range. The frequencies belowthe audible range which constitute the volume signals, mentioned above,pass through the low pass filter 15 which does not admit the frequenciesin the audible range.

The main signals after passing through the filter 70 are furtheramplified in the circuit con taining the triode 12, the battery 13,battery H and transformer 14 and from thence to the loud speaker throughthe lines 96 and 91.

The volume signals after passing through the low pass filter 15 areamplified in the circuit consisting of the pentode [1, battery 18,battery 76 and transformer 19. This pentode 11 is charged with a lowplate voltage low screen voltage and a high grid signal voltage so thatthe amplification is always in excess of the capacity of the tube.Additional amplification circuits may be included between the pentode 11and the low pass filter 15, or regenerative amplification may be' usedto amplify the volume signals to tube capacity. This enables the tube tomaintain an output of constant amplitude irrespective of the amplitudeof the volume signal, provided volume signals are being transmitted bythe broadcasting station.

From the transformer 19, these volume signals pass through a correctorcircuit consisting of the triode 80, battery 8|, battery 82, resistance83, condenser 84, inductance 85, and resistance 86. The condenser 84 isof suilicient capacity to transmit the volume signals of lowestfrequency. This circuit varies the drop in voltage across the resistance86 inversely to the frequency of the volume signals. The higherfrequencies are choked by the impedance of the coil 85 and are dividedbetween this coil and the resistance 83, the lower the frequency alarger proportion of the current passes through the-coil 85 and theresistance 86. Connected across the resistance 86 is a rectifyingcircuit consisting of the diode 87,

resistance 89, which is lay-passed by the condenser 88. Therectification of these low frequency signals produces an envelope inwhich the amplitude varies with the frequency of the volume signals.

In a similar manner the audio signals from the transformer T4 arerectified in the circuit containing the diode 9i, and resistance 93,which is by-passed by the condenser 92. This produces an envelope theamplitude of which varies with the voltage of the audio signals, thesesignals being transmitted to the loud speaker by the lines 96 and 91.

The envelope produced by the diode 9| varies in amplitude with theamplitude of the signals as actually received.

The envelope produced by the diode 81 varies inversely as the frequencyof the volume signals sent out by the broadcasting station. If thecircuits are properly adjusted the two envelopes should be practicallythe same in amplitude at all times. The positive ends of the resistances89 and 93 are connected to each other. The negative end of resistance 89is connected by the wire 94 to the filaments of pentodes 54 and 59. Thenegative end of resistance 93 is connected by the wire 95 to the gridsof the pentodes 54 and 59. By these connections the drop in voltageacross the resistor 89 is compared with the dropin voltage across theresistor 93. The drop in voltage across the resistor 89 varies with thevarying voltage of the envelope in that circuit and is representative ofthe strength of signals as transmitted. The drop in voltage across theresistor 93 varies with the varying voltage of the envelope in thatcircuit and isrepresentative of the strength of the signals as received.If the en vclope of the signals as actually received has greateramplitude than the envelope of the volume signals, the grids of thepentodes 54 and 59 will be made more negative by the connection to thenegative side of resistance 93 and the volume of the received signalswill be reduced until the amplitude of the two envelopes are equal.

If the envelope of the volume signals as produced by the diode 81 isgreater than theenvelope of the signals actually received, the filamentsof the pentodes 54 and 59 will be made more negative with reference tothe grids, which increases the grid voltage and increases the volume ofthe received signals until the envelopes are equal.

The operation of these circuits may be summarized as follows: In thetransmitting set the signals are amplified and then rectified in thediode [0 so as to produce an envelope, not of the signal itself but ofits amplitude.

This direct current which varies with volume of sound to be transmittedis used to vary the frequency of the oscillating tube 19. Theoscillations of this circuit are combined with the oscillations on thecircuit of triode 30, inwhich the oscillations are constant. The beatsof these two oscillating circuits are rectified in the circuit of thetriode 33, passed through the low pass filter 36 and connected to thetransmitter modulator.

The beats of these circuits-are of such low frequency as to not beaudible, or interfere with the modulation of the carrier fortransmission of the regular signals.

In the receiving set after the signals have been amplified and detectedin the usual manner, the audio frequencies are divided, the audiblefrequencies passing through the filter l0 and after furtheramplification to the loud speaker. The 75 audio frequencies below theaudible range are the volume signals, these are amplified in a tube 11which is overloaded so that the amplitude of these signals is notproportional to the strength. of the signals received but is fixed bythe capacity of the tube. v v

These volume signals are then passed through the corrector circuit ofthe 'triode 80 by which their amplitude is made inversely proportionalto their frequency, and they are then rectified in' the circuit of thediode 8i! as mentioned above. The voltage of this circuit forms thestandard by which the volume is to be controlled. By

connecting lines 94 and 95 to the grids and fila ments of several stagesof amplification, a close regulation of volume may be automaticallyobtained in tuning from one station to another, if these stations areprovided with volume signals.

As mentioned on page 1, a purpose of this in ,vention is to make thevolume of the sound re ceived'proportional to the sound transmitted. Itincludes means for correcting distortion in volume from all causes inelectrical transmission and reception, such distortion as iscaused bythe curvature of the grid voltage, platecurrent curve of the. tubes usedin audio frequency amplification. It also includes means for limitingthe noise received, so that the volume of the noise plus the volume ofthe signal received would be equal to what the volume of the signalshould be if noise were not being received.

This invention is shown and described as referring to the transmissionand reproduction of electrical signals which represent sound signals.

.It is apparent that it may be applied to electrical "signals whichrepresent other forms of intelligence signals besides sound, and it isintended to include the control of electrical signals which are used totransmit intelligence in any form.

I claim:

1. In an electrical receiving set, means for re,

ceiving a carrier wave, means for receiving intelligence signals bydemodulating said carrier wave, means for receiving signals whichindicate the volume of the sound being transmitted and meansforcomparing an intensity derived from said intelligence signals asreceived. with the I volume of sound transmitted as indicated by saidvolume signals, means for using said comparison for correcting the rateof amplification of said intelligence signals.

2. In an electrical receiving set, means for receiving signals whichvary in frequency with the volume of sound transmitted, means forproducing an envelope derived from said volume signals which varies inamplitude in proportion from said carrier medium, deriving said addi--tional modulating current from said carrier medium, comparing thestrength of said signals with the strength of the signals transmitted asrepresented by said additional modulating current, and controlling thedegree of amplification of said signals by a voltage which correspondsto the difference between the strength of said sig- Arectified signalsto control the degrees of using saidcomparison to control the rate ofamnals as received and the strength of said signals, when transmitted,as represented by said additional modulating current.

'4. The steps in a method of deriving signal energy froma carrier mediummodulated, with electrical signals andan additional modulating currentwhich comprise, deriving from said carrier medium said electricalsignals, deriving from the carrier medium said additional modulatingcurrent, amplifying'said modulating current to a fixed amplitude,amplifying said modulating current to produce a difference. of potentialwhich varies in accordance with the variations of frequency of saidmodulating current, rectifying said differences of potential, rectifyingsaid electrical signals, using the-comparative strength of saidrectified difference of potential and said plification of said signals.5'

5. In-an electrical receiving set, means for receiving sound signals,means for receiving control signals which represent by their frequency athe volume of the sound being transmitted,

means for rectifying said control signals-means for obtaining potentialsfrom said control signals which vary with their frequency, means foramplifying said sound signals, means for regulating I said amplificationby said potentials, meansfor rectifying said sound signals and obtainingpotentials representing their amplitude,,me'ans for comparing thepotentials representing the volume of said amplified signals with thepotential" representing the volume of sound transmitted as representedby said control signals.

6. In an electrical receiving set, means for receiving a carrier wavemodulated with sound signals, means for deriving sound signals'frornsaid carrier wave, meansfor amplifying said sound signals, .means forobtaining a voltage proportional to the volume of said amplified soundsignals, means for deriving control sig nalsof variable frequency fromsaid carrier wave, means for obtaining a voltage which varies with thefrequency of said control signals, means for controlling saidamplification by ence between said voltages.

, 7. In an electrical receiving set, means for receiving a carrier waveof constant frequency containing sound signals and also signalsrepresent ing the volume of sound transmitted, means for thedifferderiving sound signals from said carrier wave,

means for deriving'potentials from said carrier wave which represent thevolume of sound being transmitted, means for comparing the potentialsrepresenting the volume of sound as received with the potentialsrepresenting the volume of sound transmitted'as indicated by said volumesignals, means for using said comparison for coni trolling'theamplification of said carrier.

8. In an electrical receiving set, means forreceiving a carrier wavemodulated with sound signals, means forderiving sound signals fromsaidcarrier 'wave which vary in frequency over the whole audio-frequencyband, means for am- I plifying said sound signals in said'receiving set,

at all of said frequencies, means for deriving volume signals from saidcarrier wave which represent the volume of sound being transmitted,means for comparing the potentials representing the volume of said soundsignals as amplified at all audio frequencies, with the potentialsrepresenting-the volume of sound being transmitted as indicated by saidvolumesignals, means for plification of said sound signals.

9. In an electrical receiving set,n1e'ans for recciving signals whichrepresent the volume of the sound being transmitted, means foramplifying said signals to a constant amplitude, and means for comparingthe potentials representing the volume of sound as received with thepotentials representing the volume of sound transmitted as indicated bysaid signals, means for using said eompar'son to control the volume ofsound received.

10. In an electrical receivin set, means for receiving a carrier wavecontaining control signals and intelligence signals, means forrectifying said carrier wave, means for deriving intelligence signalsfrom the modulation of said carri vave, means for amplifying saidintelligence signals, means for obtaining a voltage representa-tive ofthe amplitude of said intelligence signals, means for comparing saidrepresentative voltage with a voltage derived from said control signals,and means for utilizing the difference between s:- d voltages toincrease and decrease amplification of said signals.

11. In an electrical receiving set, means for receiving a car Wave whichmodulated a frequency control and with sound signals, means forrectifying said carrier wave, means for deriving signals from themodulation of said carrier wave, means for amplifying said signals,means i obtaining a voltage representative of the amplitude of saidsignals, means for comparing said representative voltage with a voltageto which it is desired for the signals to be amplifled, and nieares forregulating the amplification of said signals, so that their voltage willcorrespond with said desired voltage.

12. In an electrical receiving set, means for receiving a carrier wavewhich is modulated with frequency control and with sound signals, meansfor rectifying said carrier wave, means for deriving sound signals fromthe modulation of said carrier wave, means for amplifying said signals,means for obtaining a voltage representative of the amplitude of saidsignals, means for comparing said representative voltage with a voltagederived from said frequency control to which it is desired for saidsignals to be amplified, and automatic means for increasing the amplifieSon of said signals when said representative voltage is less than saiddesired voltage.

13. In an electrical receiving set, means for receiving a carrier Waveof substantially content frequency which contains intelligence sig- '51d volume control signals, means for decl control signals from saidcarrier, '1 deriving said intelligence signals from said ca:. ler, meansfor utilizing said control signals in combination with said intelligencesignals to control the rate of amplification of said carrier.

In an electrical receiving set, means for receiving intelli ence signalsand control signals which indicate by their frequency the volume of heintelligence signals transmitted, means for obtaining potentialsrepresenting the amplitude of said intelligence signals, means forobtaining potentials representing the frequency of said control signals,means for controlling the etc of amplification of said intelligencesignals by the combined action of said potentials.

15. In an electrical receiving set, means for receiving a carrier waveof substantially constant frequency which contains intelligence signalsand control signals which indicate by their frequency the volume of theintelligence signals transmitted, means for obtaining potentialsrepresenting the amplitude of said intelligence signals, means forobtaining potentials representing the frequency of said control signals,means for controlling the rate of amplification of said carier by thecombined action of said potentials.

16. In an electrical receiving set, means for receiving a carrier Waveof substantially constant frequency which contains intelligence signalsand control signals which indicate by their frequency the volume of theintelligence signals transmitted, means for obtaining potentialsrepresenting the amplitude of said'intelligence signals, means forobtaining potentials representing the frequency of said control signals,means for controlling the rate of amplification of said carrier by thedifference between said potentials.

17. The steps in receiving a carrier wave of substantially constantfrequency, modulated with intelligence signals, and modulated withcontrol of variable frequency, which comprise, deriving saidintelligence signals from said cariier, obtaining potentialsrepresenting the amplitude of said intelligence signals, deriving saidcontrol signals from said carrier, obtaining potentials representing thefrequency of said control signals, regulating the rate of amplificationof said carrier by the combined action of said potentials.

18. The steps in receiving a carrier wave of substantially constantfrequency, modulated with intelligence signals and control signals ofvariable frequency, which comprise, deriving said intelligence signalsfrom said carrier, obtaining potentials representing the amplitude ofsaid intelligence signals, deriving said control signals from saidcarrier, obtaining potentials representing the frequency of said controlsignals, regulating the rate of amplification of said intelligencesignals by the combined action of said potentials.

, 19. The steps in receiving a carrier Wave of substantially constantfrequency modulated with intelligence signals, and modulated withcontrol signals of variable frequency, which comprise, deriving saidcontrol signals from said carrier, amplifying said control signals to aconstant amplitude, obtaining potentials which represent the frequencyof said control signals obtaining po tentials representing the amplitudeof said intelligence signals, regulating the rate' of amplification ofsaid intelligence signals by the difference between said potentials.

20. A method of receiving and amplifying electrical signals whichcomprises, receiving intelligence signals, receiving control signalswhich indicate by their frequency the volume of the intelligence signalstransmitted, obtaining potentials representingthe amplitude of saidintelligence signals, obtaining potentials representing the frequency ofsaid control signals, controlling the rate of amplif cation of saidintelligence signals by the combined action of said potentials.

JAMES L. GETAZ.

